An electric motor generally comprises a rotor, stator, and casing. The stator comprises a laminated iron-core (laminated core of silicon steel plates) and end plates and a casing which fasten the laminated core. As the casing a cast casing provided with cooling fins is used. Miniaturization, direct iron-core cooling, and cost reduction considerations, however, have resulted in development of electric motors without cast casing and with exposed iron-cores. The elimination of cast casing and other casings, however, makes laminated iron-core susceptible to deformation by sliding of the laminated plates. Accordingly, it is necessary to provide a means for securely fastening a laminated iron-core. Methods of fastening include the method of boring holes through the laminating iron-core (laminated silicon steel plates) and of binding it with bolts and the method of making longitudinal grooves for welding in the outer periphery of the laminated iron-core and performing arc welding. In the former case, there is the danger of twisting of the laminated iron-core. In the latter case, there is the danger of unsecure joining of the steel plates constituting the laminated iron-core. Attempts have been made to securely fasten the laminated iron-core by forming square longitudinal grooves in its outer periphery, inserting square bars into the square grooves by, e.g., hammering, and then welding together the laminated iron-core and square bars. In this case, during the arc welding process, the still unwelded end portions of the square bars bend up and rise over the outer surface of the iron-core due to thermal deformation. This makes it necessary to remove the risen end portions of the square bars by machining. Furthermore, the weld strength of the weld zone including the machined portions of the square bar is thus lower than that of the weld zone including the rest of the square bar.